Atrophy in multiple system atrophy relates to mitochondrial and oligodendrocytic processes

ObjectiveTo investigate the gene expression and neurobiological underpinnings of brain atrophy in multiple system atrophy (MSA) using imaging transcriptomics and PET-based molecular annotation. MethodsWe derived brain atrophy measurements from the T1-weighted MRI scans of 65 patients with MSA and 181 age- and sex-matched healthy controls. Using postmortem data from the Allen Human Brain Atlas, partial least square (PLS) regression was used to identify gene expression components associated with atrophy. Gene enrichment analyses were performed to investigate the biological processes with enriched genes in regions showing atrophy. Annotation mapping was used to identify the neurochemical systems whose density maps matched atrophy in MSA. ResultsAtrophy in MSA was found to primarily affect deep brain regions, including the cerebellar white matter, pons, putamen, olive nuclei, and substantia nigra. PLS regression on deep brain region atrophy identified two gene expression latent variables, explaining 27.5% of the covariance. Regions with greater atrophy overexpressed genes related to the mitochondrial respiratory chain, particularly proton transmembrane transport and complex I assembly. In addition, cell type analysis revealed that regions with atrophy overexpressed genes related to oligodendrocytes. These patterns were distinct from those found in Parkinsons disease. Atrophic regions in MSA also displayed less serotonin and GABA receptors and more acetylcholine and noradrenaline receptors. InterpretationRegions showing atrophy in MSA show specific features, namely overexpression of genes related to mitochondrial function and oligodendrocytes and distinct neurochemical patterns. This study highlights some of the biological and neurochemical mechanisms underlying selective vulnerability of brain regions in MSA.